This research project represents an integrated multidisciplinary approach to the study of the response of central catecholaminergic and serotoninergic systems to neonatal undernutrition, nutritional rehabilitation, and adult stress. The nutritional model involves the feeding of low protein diets (12% casein) to rat mothers during lactation. This regimen results in marked retardation of body and brain growth. Endogenous levels of norepinephrine, dopamine, and serotonin, tyrosine hydroxylase, dopamine-beta-hydroxylase, and tryptophan hydroxylase were measured in various brain regions during periods of chronic undernutrition and nutritional rehabilitation. Differential changes in neurotransmitter levels and synthesis enzymes were observed in specific brain areas, the changes dependent on the specific region and age at which rats were studied. Current studies are investigating catecholamine and serotonin turnover in rats subjected to acute and chronic foot shock and swim stress. Additional studies involve the assessment of amino acid transport of neurotransmitter precursors, serotonin receptor binding, and behavioral pharmacological studies. This project seeks to define the neurochemical mechanisms that may underly the observed hyper-responsivity of previously malnourished animals when subjected to novel and stressful situations in adult life.